void foo(std::string arg, ...) {
// do something with every argument
}
Lets say I want to be able to take every string argument and append an exclamation mark before printing it out on a new line.
3 Answers
The best way is to use parameters pack. For example:
#include <iostream>
// Modify single string.
void foo(std::string& arg)
{
arg.append("!");
}
// Modify multiple strings. Here we use parameters pack by `...T`
template<typename ...T>
void foo(std::string& arg, T&... args)
{
foo(arg);
foo(args...);
}
int main()
{
// Lets make a test
std::string s1 = "qwe";
std::string s2 = "asd";
foo(s1, s2);
std::cout << s1 << std::endl << s2 << std::endl;
return 0;
}
This will print out:
qwe!
asd!
2 Comments
James
thanks yaranov, is there an iterative way to do this? I'm asking because I want to define a function/api that converts a list of strings into a single comma separated string. and it seems like a stringstream with a loop is the most efficient way.
stas.yaranov
If you have a list of strings then first if you need to modify strings then you can use
foo accepting single argument for each string in a list (each item is going to be modified since argument to foo is passed by reference) and second is to create a new string by joining strings in the list by using something like join from boost (boost.org/doc/libs/1_60_0/doc/html/boost/algorithm/join.html).C++17
Use a parameter pack with a fold expression:
#include <iostream>
#include <string>
// Modify multiple strings. Here we use parameters pack by `...T`
template<typename ...T>
void foo(T&... args)
{
(args.append("!"),...);
}
int main()
{
// Lets make a test
std::string s1 = "qwe";
std::string s2 = "asd";
foo(s1, s2);
std::cout << s1 << std::endl << s2 << std::endl;
return 0;
}
answered Sep 15, 2020 at 5:08
Fake Code Monkey Rashid
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Comments
Here is an iterative solution. There is a bit of noise in the function call, but no computation of the number of varargs is needed.
#include <iostream>
#include <string>
#include <initializer_list>
#include <functional> // reference_wrapper
void foo(std::initializer_list<std::reference_wrapper<std::string>> args) {
for (auto arg : args) {
arg.get().append("!");
}
}
int main() {
// Lets make a test
std::string s1 = "qwe";
std::string s2 = "asd";
foo({s1, s2});
std::cout << s1 << std::endl << s2 << std::endl;
return 0;
}
printfformat string. You can solve it by passing an extra first integer argument whose value is the number of string arguments. Or since you program in C++ you can use templates and parameter packs.